1. Field of the Invention
The present invention relates to a layout of an integrated driving circuit for driving a display apparatus.
2. Description of the Related Art
As a representative example of a flat display apparatus, for example, a liquid crystal display apparatus is known, has characteristics such as thin thickness and low power consumption, and is widely in use as a monitor for a mobile phone, a monitor for a personal digital assistant, a monitor for a computer, a monitor for a television, etc.
In such a liquid crystal display apparatus, an active matrix display apparatus in which a switching element such as thin film transistor (herein after referred to as “TFT”) is provided as a circuit in each pixel and display is controlled for each pixel can realize a high resolution, high quality display, and the use of the active matrix display apparatus in various devices is currently expanding.
FIG. 1 conceptually shows an active matrix liquid crystal display apparatus which is proposed, for example, in JPA2001-282164 (hereinafter referred to as “Reference Document 1”). The liquid crystal display apparatus (LCD) comprises a liquid crystal display panel (hereinafter referred to as “LCD panel”) 400 in which liquid crystal is sealed between a pair of substrates, a driving circuit 500 which generates a signal for driving the LCD panel 400, and a power supply circuit 600.
The LCD panel 400 is an active matrix LCD panel in which a TFT is provided as a switching element in each pixel. At a peripheral portion of a display section of the panel, a vertical direction driver which sequentially controls a gate line and a horizontal direction driver which supplies display data to a data line at a predetermined timing are formed.
The driving circuit 500 comprises a timing signal generator 510, a display data processor 520, and a digital-to-analog (D/A) converter 580. The timing signal generator 510 generates various timing signals based on various signals supplied from outside such as synchronization signals (Hsync, Vsync), and a clock signal (DOTCLK). The display data processor 520 is a circuit which processes a color video signal from outside. The display data processor 520 converts, for example, a serial digital video signal supplied from outside into a parallel signal, executes a signal process such as γ correction, and generates display data suitable for realizing a display on the LCD panel 400.
A resistor-string type converter may be used as the D/A converter 580. The D/A converter 580 converts a digital display data signal processed by the display data processor 520 into analog display data for each of R, G, and B, and the obtained analog display data is supplied to the data line of the LCD panel 400 through an amplifier or the like.
The power supply circuit 600 comprises a charge-pump circuit or the like, and generates a plurality of power supplies (power supply voltages) necessary in the display apparatus using a reference voltage supplied from outside and based on a power supply clock signal generated by the timing signal generator 510 of a logic section. The power supply circuit 600 is used not only for the power supply of the LCD panel 400, but also for the power supply of the D/A converter 580 of the driving circuit 500.
In the display apparatus of FIG. 1, the driving circuit 500 and the power supply circuit 600 are independently integrated as external circuits of the LCD panel. In order to further improve the functions of the display panel or reduce the space for the overall device including the display apparatus, attempts have been made to integrate the driving circuit 500 and the power supply circuit 600 as a driving apparatus for the display apparatus and mount the integrated driving circuit on the panel 400 using, for example, a COG (Chip On Glass) technology.
In order to mount such an integrated driving circuit on the LCD panel 400, the integrated driving circuit must be placed at a peripheral portion of the panel other than the display section in order to not reduce an area of the display section. Therefore, the integrated driving circuit must be formed in an elongated shape along a row direction (horizontal scan direction) or a column direction (vertical scan direction) of the display section.
FIG. 2 shows a layout of the elongated-shaped integrated driving circuit 700. From the viewpoint of a layout efficiency, circuit elements having similar functions are generally formed at positions close to each other, and, thus, the timing signal generator 510 and the display data processor 520 of FIG. 1 which can be formed using logic circuit elements are collectively placed as a logic section 501. In addition, the power supply circuit 600 comprising a capacitor and a switch or the like (in the case of a charge-pump type power supply circuit) and the D/A converter 580 comprising a divided resistor and a switch or the like (in the case of resistor-string type D/A converter) are formed in collective regions.
A power supply clock signal for generating a power supply must be supplied from the logic section 501 to the power supply circuit (DC/DC converter) 600, and, thus, it is desirable that the logic section 501 and the power supply circuit 600 be placed close to each other. In addition, because the analog display data to be supplied to the LCD panel 400 significantly affects the display quality, a small variation in the voltage is required for the analog display data. In addition, a large amplitude is required for the analog display data because of an operation characteristic or the like of the TFT in the LCD panel 400. Thus, in order to minimize the voltage drop, the power supply circuit 600 and the D/A converter 580 must be placed as close to each other as possible. Therefore, in the integrated driving circuit 700 of the related art, as shown in FIG. 2, the power supply circuit 600 is placed at a center portion along a longitudinal direction of the integrated driving circuit 700 having an elongated shape, and the logic section 501 and the D/A converter 580 are placed in contact with the power supply circuit 600 at left and right end regions of the integrated driving circuit 700.
With the circuit layout of the related art as shown in FIG. 2, a line distance between the logic section 501 and the power supply circuit 600 and a line distance between the power supply circuit 600 and the D/A converter circuit section 580 can be minimized. However, a line from the logic section 501 to the D/A converter circuit section 580 must pass through a formation region of the power supply circuit 600. Here, a large number of data lines corresponding at least to a number of bits of the digital display data and a number of colors are required from the logic section 501 to the D/A converter circuit section 580. In other words, a very large number of data lines must be provided in the formation region of the power supply circuit 600 in parallel to each other, and, thus, the area along the line width direction cannot be easily reduced.
In addition, because it is required to output necessary signals to the power supply circuit 600 and the D/A converter circuit section 580 with a minimum line length, all output sections must be placed in a region of the logic section 501 at a side near the power supply circuit 600. Thus, the output sections are unevenly distributed on one side of the logic section 501, and, it is difficult to improve the layout efficiency in the logic section 501.
On the other hand, because the integrated driving circuit 700 is mounted on the panel, the integrated driving circuit 700 must be designed to fit in a very limited region with a narrow width in a peripheral portion of the display section. However, the layout efficiency of the driving circuit 700 of the related art is low, and it is difficult to reduce the width along the short side direction, which makes it difficult to reduce the size of the panel 400.